Topic: Air Quality
Dr. George Mwaniki is an air quality expert within UNEP’s Division of Technology Industry and Economics. He is currently working on the UNEA’s resolution to strengthen UNEPs role in air ...

Hi Dr George. do planting of trees improve air quality? and can you urge for a bill to make people with idle land plant indigenous trees by law. would also like to know more on carbon credit. thanks

Ng'ang'a mwaniki (from Kenya)

Dear Mr. Mwaniki,Many thanks for your question. Planting of tress, for the most part contributes to cleaner air. However, in urban areas where vehicular emissions are considerably high, the choice of trees to be planted is critical. Studies have shown that, trees also emit organic compounds called Biogenic Volatile Organic Compounds (BVOCs). When these compounds are emitted in an urban air shed, they react with vehicular emissions to form ozone, which is an air pollutant with detrimental health effects to both humans and ecosystems. So in short, when planting trees in urban areas, trees that emit least BVOCs would be ideal. But for rural areas, trees would be a plus in regard to air quality. Planting indigenous trees is always a plus, although it might have its own disadvantages as some of these trees take a long time to mature. On the issue of carbon credits, I am not an expert on this so let me avoid stay clear off this, but please do go to our website there is a lot of good information on this.

Posted on 31/07/2015 04:41:26

Dear Dr. Mwaniki,Having read your profile, I assumed that you were involved in a research that studied Atmospheric Brown Clouds (ABCs) on Mount Kenya. Indeed, I had thought that the ABCs were largely confined in Asia. What has been the impact of the ABCs on the local climate around Mount Kenya? My understanding is that the Atmospheric Brown Clouds formed from sulphate aerosols tend to cool temperatures in the troposphere by masking/reflecting the sunlight. Therefore, efforts being undertaken to encourage the use of cleaner transport and reduce the amount of sulphur in fuels have been unmasking the warming of sunlight thus increasing temperatures in the troposphere. Besides, Atmospheric Brown Clouds formed from soot aerosols tend to absorb insolation, thus warm temperatures in the troposphere.

Francis Bagambilana (from Tanzania (United Republic of))

Dear Francis,Many thanks for your question. You are quite right that ABCs are largely associated with Asia; but this does not mean they are confined there. In previous studies, substantial loadings of ABCs over Eastern USA and Europe have also been observed; mostly during summer time months when these areas experience reduced precipitation. During the Mount Kenya ABCs study, our main aim was to assess the level of regional and subregional black carbon emissions. From the study we saw substantial black carbon emissions from the region and this is expected to increase in the future, thus ABCs concentration in the region will be a major climate driver in the future. During this study we did not concentrate on sulphates and nitrates and their role in driving ABCs’ concentration, this is mainly because black carbon emissions from the region are known to be the most important drivers of ABCs. Maybe this will change in the future as economic and population growth increase the emissions of both NOx and SOx, although it is also important to mention that the region has made substantial efforts towards low sulfur fuels. So I do hope future studies will also look at the effect of these other important drivers.